Converting into PDO - php

Question

Good evening everyone!
I need your help again. Please bear with me because I am very new to this. Hoping for your understanding. So, I am having a project on oop and pdo. I am having quite hard time converting this into pdo.. Here is my code..
bookReserve.php
while($row=mysql_fetch_array($sql))
{
$oldstock=$row['quantity'];
}
$newstock = $oldstock-$quantity;
Here's what i've done
while($row = $code->fetchAll())
{
$oldstock=$row['quantity'];
}
$newstock = $oldstock-$quantity;
Is that even correct?
And for the oop part, after this while loop I have a query to execute.
$sql="update books set no_copies = '$newstock' where book_title = '$book_title'";
Here's what I've done trying to convert it into pdo
public function bookreserve2($q)
{
$q = "UPDATE books SET quantity WHERE = $newstock where book_title = '$book_title'";
$stmt = $this->con->prepare($q);
$stmt->execute(array(':newstock'=>$newstock));
$result = $stmt->fetch(PDO::FETCH_ASSOC);
return $result;
}
Again, Is that even the correct converted query?
and how would I call $newstock?
P.S. my oop class and pdo is placed in a separate file. Thought this might help.
Thanks

Answer 1

You are not including your query parameters in your function, and your query has syntax errors (extra WHERE) and you are directly inserting your values not using placeholders.
It should look something like -
public function bookreserve2($newstock,$book_title)
{
$q = "UPDATE books SET quantity = :newstock WHERE book_title = :book_title";
$stmt = $this->con->prepare($q);
$stmt->execute(array(':newstock'=>$newstock,':booktitle'=>$book_title));
if($stmt){
return true;
}
else {
return false;
}
}